1. Field of the Invention
This invention relates to an inkjet recording head and a manufacturing method thereof, and an inkjet recording apparatus in which ink droplets are ejected according to image information onto a recording medium for recording.
2. Description of the Related Art
Recently, the inkjet recording apparatus has attracted attentions as the low-cost high image quality color recording apparatus. There have been, for example, a piezo-type ink jet recording head that ejects ink from a nozzle with pressure generated by mechanically deforming a pressure chamber by use of piezoelectric material and a thermal type inkjet recording head that ejects ink from a nozzle with pressure generated by supplying a current to a heating element disposed on individual flow passage to thereby evaporate and expand ink.
In the case of these inkjet recording heads, a head chip on which an ink discharge mechanism for discharging ink droplets is mounted is jointed to the tip end of an ink supply member. In detail, ink is supplied from a tubular passage of the ink supply member to an ink supply opening of a head chip, and the ink is discharged from a nozzle.
In the case of the above-mentioned thermal type inkjet recording head, ink droplets are ejected onto a medium from a nozzle correspondingly to an image signal for recording. The driving force for ejecting ink droplets from a nozzle is generated by applying an electric pulse to an electric-heat conversion element (heat generator) to generate heat from the heat generator to thereby generate bubbles, and the bubbles causes pressure and the pressure functions to eject the ink droplets.
The schematic exemplary structure of an inkjet recording head is described herein.
The inkjet recording head is provided with a head chip having an ink discharge mechanism, for example, as shown in FIG. 4. As shown in FIG. 5, the head chip includes an ink discharge mechanism having at least a nozzle (discharge opening) 18 for ejecting ink droplets, an individual flow passage (ink flow passage) 20 for supplying ink toward the nozzle 18 that has the nozzle 18 at the one end, a pressure generation;.section 24 disposed on individual flow passage 20 having the pressure generation plane positioned in parallel to the ink flow that flows in the nozzle direction in the flow passage, and a common liquid chamber 22 disposed commonly to plural individual flow passages 20 for supplying ink to the individual flow passage, and additionally having an ink supply opening 26 for supplying ink from the external to the common liquid chamber 22 as required in some cases. In this case, the common liquid chamber 22 temporarily holds ink supplied from an external ink tank. The common liquid chamber is also served as a part of the liquid tank, and the tank is commonly connected directly to plural individual flow passages 20 so that ink is supplied to the individual flow passages 20.
In such an inkjet recording head, the pressure generation surface of the pressure generation section 24 is disposed in parallel to the ink flow that flows in the flow passage, and ink droplets are ejected from the nozzle into the direction perpendicular to the normal line of the pressure generation surface (side direction) (side ejecting type head).
A side ejecting type inkjet recording head as described hereinabove is manufactured from a substrate formed by joining an element substrate (equivalent to the above-mentioned pressure generation side broad) and a liquid flow passage substrate (equivalent to the above-mentioned flow passage substrate) as described in the Japanese Published Unexamined Patent Application No. Hei 11-227208.
The manufacturing process will be described in detail hereunder. An ink supply opening and an ink chamber (common liquid chamber) that are served for supplying ink from the external ink tank to an ink jet recording head are formed on a liquid flow passage substrate by means of wet anisotropic etching, and an individually formed ink flow passage (individual flow passage) is formed with high accuracy by means of reactive ion etching. In the case where a recess (recess 43 shown in FIG. 9 of the Japanese Published Unexamined Patent Application No. Hei 11-227208) is formed on a heating resistor, it is formed by means of wet anisotropic etching. On the other hand, a heating resistor (pressure generation section), an electrode, and a driving element are formed on the element substrate. The above-mentioned liquid flow passage substrate and element substrate are positioned fittingly and joined, and cut (diced) and separated into individual inkjet recording heads by use of, for example, a dicer. At that time, a nozzle (discharge opening) for ejecting ink droplets is formed by cutting at a predetermined dicing position by means of dicing.
However, in the case of the recording apparatus that ejects liquid from a nozzle, the configuration of ink droplet to be ejected and the ejecting performance depend on the flow passage length if the cross-sectional area of the ink flow passage (individual flow passage) having a nozzle at the one end is constant, the fluid resistance depends on the length. of the flow passage, and as the result it is impossible to keep the drop quantity (drop volume) of a ink droplet constant if the flow passage length is not constant.
In other words, if the cutting position deviates from the dicing position when a nozzle (discharge opening) is formed by dicing as described hereinabove, the drop volume changes and the liquid drop size changes irregularly, and as the result the high quality image cannot be obtained.
However, it is difficult to position the cutting position more accurately because the cutting involves a process of several xcexcm order range, therefore the cutting process is involved in a problem with stabilization of high quality and obtaining high quality image. On the other hand, because the positional deviation as described hereinabove affects adversely on the image quality significantly, a process for checking the dicing position after cutting process is required and many inspection processes are required, and furthermore only the head chips that have passed the inspection for rejection of off-specification product are used, as the result the rejection results in the high cost of the accepted products.
Japanese Published Unexamined Patent Application No. Hei 7-156411 discloses an inkjet printing head for ejecting ink droplets in the normal line direction of the heating surface of a heater served as a heating body having the structure in which the cross-sectional area of the circular cross section of the nozzle part is curved outward in a curved surface from the center of the circular cross section of the flow passage increasingly from the minimum inside diameter part of the flow passage through which ink flows toward the nozzle discharge side direction. In the Patent Application, the suppression of printing quality due to meniscus vibration after refilling is described, but the length of the nozzle part of the inkjet printing head described herein is determined by the plate thickness, and the relation between the length and the drop volume of a ink droplet is not described. In other words, in the case of the curved structure in which the flow passage is curved from the center toward the outside, it is difficult to reduce the change of the drop volume of ink droplets corresponding to the flow passage length difference and to keep the drop volume of ejected ink constant. As the result, it is impossible to resolve the problem in the manufacturing process and the problem of high cost due to the deviation of the cutting position as described hereinabove.
In the case where plural nozzles for ejecting ink droplets are formed by use of a dicer or the like as in the case of the above-mentioned side ejecting type inkjet recording head, it is quite difficult to cut without any deviation of the cutting position. A method has not been known that is used for forming nozzles stably so that the length of the flow passage having a nozzle at the one end is controlled within a range in which the configuration of ejected ink droplets and the ejecting characteristics are not affected adversely.
The present invention has been made in view of the above-mentioned circumstances and to solve the above-mentioned problem, and provides an inkjet recording head that is capable of compensating the change of drop volume due to the deviation of the cutting position in dicing or the like when cutting and forming a nozzle, and ejecting ink droplets of a constant drop volume independently of the flow passage, which inkjet recording head is manufactured with less manufacturing processes and with suppressed generation of off-specification products to result in low-cost products.
Furthermore, the present invention provides a low-cost inkjet recording apparatus that is capable of ejecting ink droplets of a constant drop volume to thereby form a high quality image.
Furthermore, the present invention provides a method for easily manufacturing an inkjet recording head that is capable of compensating the change of drop volume due to the deviation of the cutting position in dicing or the like, and stably ejecting ink droplets of a constant drop volume, which inkjet recording head is manufactured with less manufacturing processes and with suppressed generation of off-specification products to result in low-cost products.
The above-mentioned problem is solved by applying the followings.
An aspect of the present invention provides an inkjet recording head having a head chip on which an ink discharging mechanism is mounted, the ink discharging mechanism having at least individual flow passages each having a nozzle at one end thereof and a pressure generation part with a pressure generation plane positioned in parallel to a direction of flow of ink in the nozzle, and a common liquid chamber communicated commonly to plural individual flow passages that supplies ink to the individual flow passages. The individual flow passage has a region having a maximum cross-sectional area, a reducing region where a cross-sectional area thereof reduces from the maximum cross-sectional area to a minimum cross-sectional area, and an expansion region where a cross-sectional area thereof increases from the minimum cross-sectional area successively from the pressure generation part toward the nozzle, the regions being perpendicular to the ink flow direction.
The cross-sectional area of the expansion region may increase so as to almost offset an increase of a flow passage resistance caused by making the individual flow passage of the expansion region longer.
Alternatively, the cross-sectional area of the expansion region may increase so as to keep an ejected ink droplet volume almost unchanged even if the individual flow passage of the expansion region is made longer.
With the above configurations, the cross-sectional area of each individual flow passage extending from the region having the maximum cross section area on which the pressure generation part is provided to the nozzle, which cross section is perpendicular to the ink flow direction of the individual flow passage, is reduced from the maximum cross section area to the minimum cross-sectional area and then increased from the minimum cross-sectional area. As the result, even if the length of the flow passage of an individual flow passage having the nozzle at the one end thereof deviates from a certain specified range when nozzles that are served for ejecting ink droplets are cut and formed by dicing, the inkjet recording head can eject ink droplets having a constant drop volume stably regardless of the length of the flow passage.
Furthermore, it is not necessary to inspect the cut position and the inspection process is not necessary, the generation of off-specification products rejected during inspection is significantly suppressed, and as the result the low-cost inkjet recording head is implemented.
Also in the above aspect, the cross-sectional area of the nozzle that is formed at one end of the individual flow passage may be one to two times as large as the minimum cross-sectional area.
With the above configuration, because the cross-sectional area of a nozzle that forms the one end of an individual flow passage increases gradually from the minimum cross-sectional area to a cross-sectional area ranging from the minimum cross-sectional area to the doubled minimum cross-sectional area, it is possible to compensate the drop volume of ink droplets ejected from the nozzle so as to be constant regardless of a slight change of the flow passage length of the individual flow passage. In other words, if the cross-sectional area is different due to the different length of the flow passage, for example, if the flow passage length is longer than a predetermined value, then the liquid resistance that the ink receives is larger than the value corresponding to the predetermined flow passage length and the drop volume of ejected ink droplets is smaller than the expected value, but the increase of the fluid resistance is suppressed (compensated) because the cross-sectional area is larger than the predetermined value by a value equivalent to the increase of the fluid resistance, and as the result the drop volume is kept almost constant.
The flow rate of ink that flows in a flow passage is not affected in the above-mentioned range, and the high speed motion is not affected.
Also in the above aspect, the expansion region may include an increasing region where the cross-sectional area thereof increases in proportion to a length of the expansion region in the ink flow direction.
With the above configuration, the expansion region of an individual flow passage is provided with the increasing region where the cross-sectional area of the individual flow passage increases in proportion to the length of the expansion region in the ink flow direction, that is, the cross-sectional area increasing rate B that is assigned to the ordinate axis increases linearly with the length A in the ink flow direction of the region that is assigned to the abscissa axis (proportional relation; B=aA). Therefore, for example, the configuration of the increasing region is quadrangular pyramid-shaped if the cross-sectional configuration is rectangular, or is triangular pyramid-shaped if the cross-sectional configuration is triangular, and the configuration of the increasing region is pyramid-shaped regardless of the cross-sectional configuration. As the result, the cross-sectional area of the cross-sectional area of the increasing region increases in proportion to the length of the region in the ink flow direction at a constant rate and the increase of the fluid resistance due to the longer flow passage length is offset. In other words, because the fluid resistance of the ink is compensated correspondingly to the magnitude of the flow passage length, the drop volume is kept almost constant.
Also in the above aspect, an increasing rate of the cross-sectional area that increases from the nozzle side end of the increasing region toward the nozzle end may be smaller than the increasing rate of the cross-sectional area of the increasing region.
With the above configuration, the increasing rate of the cross-sectional area from the cross section that is the nozzle side end of the increasing region where the cross-sectional area increases proportionally at a constant rate toward the nozzle direction is gradually reduced from the increasing rate of the cross-sectional area of the increasing region. In other words, the increasing rate of the cross-sectional area decreases with increasing length as in the case of the increasing region, and finally the increasing rate is reduced to almost zero (0 less than increasing rate less than a). As the result, even in the case where the flow passage length deviates significantly from the predetermined specified value, the drop volume does not increase significantly, and an image is formed with ink droplets having a constant drop volume.
Also in the above aspect, a nozzle surface having an opening may be formed by cutting a substrate comprising a pressure generation side substrate provided with the pressure generation part and a flow passage substrate.
With the above configuration, the nozzle surface formed on the one end of an individual flow passage that ejects ink droplets is formed by cutting a substrate (head chip joined substrate) including a pressure generation side substrate and a flow passage substrate at a predetermined position. Plural nozzle openings are positioned on the nozzle surface. Because the head chip joined substrate previously having plural ink discharging mechanisms is cut at the predetermined position and plural nozzles are formed in one cutting operation, the manufacturing process can be simplified and the product is manufactured at low cost advantageously.
The present invention provides an inkjet recording apparatus provided with the inkjet recording head as described above. Because the inkjet recording apparatus is provided with an inkjet recording head described hereinabove, ink droplets having a constant drop volume are ejected stably, and a sharp and high quality image can be formed. Furthermore, a low-cost inkjet recording apparatus can be implemented because the inkjet recording head can be manufactured at low cost as described hereinabove.
According to another aspect of the present invention, a method for manufacturing an inkjet recording head has the steps of joining a flow passage substrate on which plural grooves to serve as individual flow passages to which ink is supplied and a pressure generation side substrate provided with a pressure generation part for forming a joined substrate constituting a head chip, and cutting the joined substrate to form the plural individual flow passages each having an opening at an end thereof that is served as a nozzle. Each individual flow passage has a region having a maximum cross-sectional area, a reducing region where a cross-sectional area thereof decreases from the maximum cross-sectional area to a minimum cross-sectional area, and an expansion region where a cross-sectional area increases from the minimum cross-sectional area, successively toward the nozzle, the regions being perpendicular to a direction of the ink flow in the nozzle, and each individual flow passage is cut at the expansion region by means of dicing.
The cross-sectional area of the expansion region may increase so as to almost offset an increase of a flow passage resistance caused by making the individual flow passage of the expansion region longer.
The cross-sectional area of the expansion region may increase so as to keep an ejected ink droplet volume almost unchanged even if the individual flow passage of the expansion region is made longer.
Because a flow passage is cut at the expansion region where the cross-sectional area increases gradually from the minimum cross-sectional area, even if the flow passage length deviates from a predetermined range, the cross-sectional area changes correspondingly to the change of the fluid resistance due to the change of the flow passage length as described hereinabove, and as the result an inkjet recording head that is capable of ejecting ink droplets having a constant drop volume stably can be manufactured. Furthermore, the inspection process for inspecting the cutting position can be eliminated, the generation of off-specification products is suppressed significantly, and as the result the inkjet recording head can be manufactured simply at low cost.
The present invention provides a method for manufacturing an inkjet recording apparatus in which the method for manufacturing the inkjet recording head described above is employed.